please consider showing list of apt mirrors to choose from

Debian's package managers have had this option on install since the early 2000s.

steps to find this
1) Click gear in top left hand corner
2) Software & Updates
3) Other Software tab
4) add

the window then asks for "APT line:", ie something to insert into /etc/apt/sources.list -- of course what we should be doing here is adding our own mirror from the many mirrors in places like https://launchpad.net/ubuntu/+archivemirrors - but it would be far better for this (or some) list to be provided, and for the user to click on one of the available mirrors, in addition to having the ability to manually enter an 'apt' line here.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gnome-software 3.20.1+git20160420.1.ca63436.ubuntu-xenial-0ubuntu2
ProcVersionSignature: Ubuntu 4.4.0-21.37-generic 4.4.6
Uname: Linux 4.4.0-21-generic x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CurrentDesktop: GNOME
Date: Sun Sep 4 13:48:00 2016
EcryptfsInUse: Yes
InstallationDate: Installed on 2014-07-09 (787 days ago)
InstallationMedia: Ubuntu-GNOME 14.10 "Utopic Unicorn" - Alpha amd64 (20140708)
SourcePackage: gnome-software
UpgradeStatus: Upgraded to xenial on 2016-08-16 (19 days ago)